text:
Do FAA knowledge test endorsements have an implicit expiration date? If not, can I add one explicitly?
Many things in aviation have a 60-day window. For example, a graduation certificate from an approved part 141 course is valid for the purposes of a checkride for 60 days after the date of graduation.
Suppose I endorse an (otherwise fully qualified) student to take a private pilot knowledge test, but the student doesn't take the test for an extended period (because of illness, military deployment, or whatever).  Some amount of time later, the student appears at a testing center with the endorsement in hand.  Is there a particular time limit beyond which a knowledge test endorsement is no longer valid?
If not, could I write the endorsement so that it includes a void date?  Something like:

I certify that Mr. Orville Wright has met the required training of blah blah and is prepared to take the private pilot knowledge exam. This endorsement is valid until October 31 2017.

Why add an exp date?

@acpilot - Because a student who's ready to take an exam in October 2017 is unlikely to still be ready in June 2019, but if there's no expiration date, they can still go.

I guess I just don't see the risk.

@acpilot, risk is one way to look at it, but if the instructor feels there should be a limitation, that's his choice. Probably a good thing to explain to the student, though.

As a CFI, I disagree.  It make no difference to me and only causes problems for the customer in the event that unforseen delays crop up in the course of training.  Life happens.  It's only a written test.

@acpilot - One of the criteria for renewing the certificate for a part 141 school is written exam pass rate. As an instructor, you're right, it makes no difference to you, but as a chief instructor with your school's renewal coming up later in the year, it might not be "only a written test" anymore.

@Steve V as a part 91 instructor, I do written endorsements as an AGI, rather than as a CFI, so I don't have to log results (14 CFR 61.189(b)(2))  Furthermore, you have a valid concern in that the material retention for a student will drop over time, unless ongoing study is done. Certainly over a  20 month period of time like in your comment.  As I said in my answer, you can always talk with your FSDO, but it is most likely you will hear what I did as explained in my answer.

I wondered about this myself so I asked the proctor at the CATS site where I take my exams. She couldn’t find anything that imposed a time limit. So tomorrow I am taking the Commercial Knowledge Test with an endorsement from 2001.

The last that I looked into it, there were no expiration dates on written test endorsements by CFI and GI.  However, the FAA has made it clear many times that instructors are free to add conditions to endorsements.
For example, when I endorse a student for solo, I will put limitations like:
1.Prior phone call to instructor, 2. surface winds less than 14K, and within 45 deg of runway heading, 3.Five miles vis with VFR conditions.
Of course solo endorsements have implied expiration dates. But you could endorse J Pilot for a instrument written, and add "Endorsement expires Jan 1, 2018."
Since these things are vetted regionally, if you have any concerns, you can always call the FSDO and talk with an Ops Inspector there.
I did that once when I signed a guy off for a Flight Review, and wanted a condition on the sign-off. The pilot agreed with the condition, and I ran it past the Safety Program Manager who was an Ops Inspector, and his words were, "Absolutely! Any restriction you think is appropriate is fine to add to the endorsement."  That was sometime ago, but I have no indication that the policy/latitude has changed.

Just an afterthought...as a CFI one needs to log written test results.  So that could also be a reason to not leave open ended written test endorsements.  I simply sign of all written test exams with my ground instructor certificate, which has no such log requirement.


text:
What are the benefits of buried engines?
I recently came over the de Havilland Comet, and I found an interesting feature of the aircraft: it had four engines, and all of them seemed it be embedded inside the aircraft wings. I later research about the topic, and found that they are called "buried engines". Here's a photo to better illustrate the concept:
image of de Haviland comet wing section with buried engines
Wikipedia says that "This design reduces both drag and the risk of ingesting foreign objects, but increases the difficulty of maintenance and complicates the wing structure."1. However,

I'm not sure about Wikipedia's credibility.
Wikipedia's definition is a bit too vague and broad, can anyone please explain specifically what the benefits/downsides are?

So, my question can be summarized as follows:

What specifically are the benefits of buried engines?
What specifically are the downsides of buried engines?
Why are buried engines much less common in civilian aircraft today to the point of almost never seen? I do know that some military aircraft, especially stealth bombers, have buried engines, but nearly all civilian aircraft dropped buried engines in favor of podded engines. So, why?

I appreciate any explanations! Thanks in advance!

The wiki article is not bad. It was just a bad idea in practical terms outside of specialized cases.
Buried engines play havoc with the design of wing spars because the engine and/or its ducting must accommodate the spar beam (a big hole in it typically). Doing so makes the spar quite a bit heavier. Same problem with accessibility. You need to make the bottom of the wing plank, the primary bending structure in modern torsion box wings, with a big hole in it to allow access to the engine from below or to remove it. Add it all up and the structural issues combined with poor accessibility more than cancels out any benefit drag wise.
And thus like so many ideas that look great on paper but not in the real world, it's rarely done. You stick the engines on pylons, on the wings or at the tail. Easy to get at and remove/install, and light and the wing can be a simple uninterrupted box structure.
Putting them on pylons on the wings lets them be used as counter balances for the wing itself, to move its torsional (twisting) axis forward and reducing the stiffness required of the wing box. This is why the pylons project forward. Boeing learned this on the B-47 program as they had to deal with aerolasticity problems with long flexible swept wings.

Thanks for your answer. Your answer is great and answers all of my questions. Thank you very much!

Additionally, the Comet used turbojet engines.  Newer aircraft use high-bypass turbo-fan engines.  These have a much larger diameter, so all the of the above become even more significant!

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Are pilots allowed to take laptops into the cockpit?
In response to one of my other question, a comment mentioned Northwest Airlines Flight 188, an incident where both pilots became extremely distracted after taking out their laptops. Although Flight 188 eventually landed safely without any problems, it nevertheless shows how much a pilot (or pilots, in this case) can be distracted if they start to do non-essential work on their Portable electronic devices (PEDs). This incident is a reminder of how important the sterile cockpit rule is. However, I have a question: why were the pilots even allowed to take their laptops into the cockpit? I mean, if they aren't allowed to use their PEDS for the entire flight, then there's no reason to carry them into the cockpit. Or are pilots actually not allowed to take their laptops or other PEDs in the cockpit, and that Flight 188's pilots violated this rule too? Also, are pilots today allowed to take their PEDs into the cockpit? If not, what kind of penalty may be enforced against such actions? I'll appreciate any help or explanations. Thanks in advance!

They aren't supposed to use it, but to use it once they've landed, they need to transport it right? So I don't think there would be any rule regarding having it in the cockpit.

A year earlier on Oct 1 2008, the Federal Railroad administration issued Emergency Order 26 banning non operational smart device use.  (Due to Chatsworth).  EO's are extremely rare, only one every few years.  Maybe USDOT's various administrations should read each other's highest priority bulletins.

The laptop being in the cockpit is absolutely allowed.  Having it turned on & in use during the flight for a purpose not related to the pilot's duties isn't.
In many aircraft, a pilot's bags (flight bag, suitcase, etc) are all stored on the flight deck, and it would be nonsensical to require that a laptop or other personal electronic devices be removed & stored elsewhere.  Many pilots bring laptops with them on their trips -- which can last for several days before returning home -- and use them during off-duty time for emails, movies, browsing, and so forth.  They're kept in some bag that is typically stored on the flight deck.

As of 14th April 2014 the FAA banned pilots operating under Part 121 from personal use of electronic devices and laptops while at a duty station.
Reference: The Federal Register
The rule also covers some Part 135 and Part 91 operations
Note that the rule does not prohibit the use of personal devices in connection with the operation of the aeroplane, nor does it prohibit use when not at a duty station, and for these reasons it is silent on whether the devices should be permitted on the flight deck. Specific operators may have their own rules
Note that I have not attempted to reproduce the full text of the rules here. You should take a moment to read the article linked above before asking more questions.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why do U.S. METARS give visibility in statute miles?
Training to be an ATC on VATSIM. I live in the Boston area, so I'm training with VATUSA. In the US, METAR visibility data is the only exception to 'miles' = 'nautical miles' rule (that I've learned about/am aware of).  All other use of 'miles' including speeds (knots) are in nautical miles.
It seems dangerous to have multiple standards for the same unit of measure, especially when something you want to underestimate is given in the smaller units (1NM = 1.15SM), meaning an error results in someone expecting greater visibility than they actually have (and possibly overestimating their ability to safely fly). I'm hopeful that there's a sensible reason for this, but I live in the US so I recognize it as hope as opposed to reasonable expectation.

Some other things related to weather are in statue miles as well e.g. § 91.155 Basic VFR weather minimums; Special VFR minimums; 123 Rule for IFR; Alternate visibility for IFR; Civil airport takeoff minimums.; Student Pilot visibility limitations.

The reason I've heard in the past for this is "because visibility is referring to something on the ground". That is, as opposed to in the air (or on the water) where there is no ground reference so nautical miles are used. I am afraid I do not have a reference for this.

My personal view is, that the incoherent use and mixing of standards and units (freedom units vs. oppression units etc.) is just another way to make things more complicated than they really need to be... There simply is no justification and logical reason to use all the possible units ever conceived.

Visibility is a fuzzy thing.  The 15% difference between statue miles and nautical miles is smaller than the minute-to-minute (or even observer-to-observer) variation in measurement.

In the Midwest where rural roads are often spaced exactly 1 mile apart, statue miles may be useful.

@JeffB TIL! That's pretty handy to know, actually

This page might help. Short answer appears to be “because that’s what pilots are used to.”

The U.S. METAR code is described in Federal Meteorological Handbook
(FMH) No. 1 "Surface Observations and Reports", while the U.S. TAF
code procedures used by the NWS are described in Weather Service
Operations Manual Chapter D-31. Both of these standards are tailored
to reflect existing longstanding U.S. national practices. For example,
in order to lessen the burden on the U.S. aviation community, a number
of exceptions to metric reporting units have been filed by the U.S.
Winds will continue to be reported in knots (as opposed to meters per
second), cloud layer heights, and runway visual range (RVR) will
continue to be reported in feet (as opposed to meters), visibility
will continue to be reported in statute miles (as opposed to meters),
and altimeter settings will continue to be reported in inches of
mercury (as opposed to hectoPascals).

I think you mean "because that’s what US pilots are used to*. Most of the rest of world would be used to kilometres or expect nautical miles.

Something like half of all pilots are US pilots.  And, a large number of non-US pilots trained in the US.  So, "what pilots are used to" applies on average to all pilots.

So, they use miles because pilots are used to it, and pilots are used to it because they use miles. Pretty much the same excuse as every case of the US not moving to metric!

The visibility is given in the units the meteorologists use in that region (at least externally, e.g. they may measure rainfall in mm in USA but the public gets inches). In USA it is statue miles, elsewhere it is kilometers. It is not the unit that either aviaton or surface traffic uses for speeds and navigation (some European countries use miles for cars but kilometers for visibility).
Note:
The numbers are programmed into the users (pilots) head and do not really need to exactly correspond to what is used for navigation. Fog is defined as visibility under 1 km. So one knows how 1 km visibility looks like. Certain limits (like VMC) have their values defined as round numbers in statue miles or kilometers.
Compare the situation with navigating and measiring speed in nautical miles, but measuring altitude and vertical velocity in feet. Some countries used to use kilometers for vertical velocity before 1990. And the transition to feet was very smooth. In some sense it does not matter whether it is measured in apples or in oranges. It is important that everything is consistent (within that very variable) and that one knows what is a low value, what is a high value and that the values one gets to work with are nice and round (like the flight levels from 001 to 660).

'Some European countries use miles for cars but kilometres for visibility' -- I believe 'some' means 'the UK' as the RoI has transitioned away from miles for cars to the best of my knowledge.

Distance in miles, altitude in feet makes sense because altitude is extremely important to get precise at the sub-mile scale. I'm astonished that anyone used km for it ever. Meters I could see, that's equally useful to feet (the difference between a meter and a foot isn't going to save you when it comes to separation from the ground except in action-movie sequences).

@WilliamWalkerIII Of course, I actually meant meters. But meters or kilometers is the same, really, you just move the decimal point. I never claimed anyone used whole kilometers. The precision issue is unimportant here. The point is that flight levels in feet are nice numbers and are not in meters. You could make them be nice numbers in meters, sure, but then the spacing would be impractical.

authors: Vladimir F Героям слава


text:
Is "Conflicting Traffic" any better than "All Traffic?"
CTAF guidelines make clear that "all traffic in area please advise," is a bad idea and great way to get CTAF blocked for everybody. Makes sense, cool.
I've seen in videos people using "Conflicting traffic please advise" in their initial self-announce, instead.  But is that any better, really?
I can see it both ways:
On the one hand, you're still asking for responses from an open-ended number of aircraft, all of whom could key up at once and block the CTAF.
On the other hand, if you're about to cause a runway incursion on someone who forgot to announce final... it seems like that'd be a good thing to get clear on right then and there.  What's more dangerous, a blocked CTAF, or pulling out in front of a guy on final who's too head-down to key his radio?

Some comments to answers to related question https://aviation.stackexchange.com/q/622/34686 address this issue also.

What videos do people say "conflicting traffic please advise"?

@tedder42 I don't have a URL handy atm, but the next time I see one I'll link it.

I've always considered the CTAF-announcement by itself to imply a request for "please advise".  You don't have to say what is clearly implied; it just uses up airtime and risks being misunderstood.
If someone heard you and recognizes a problem, they need to reply to you, regardless of if you use "please advise" or not.
So, in short, No, extraneous phrases that don't actually communicate information are not useful, and should be avoided.

Took the words right out of my mouth. Brevity is one key component in comms, so you make the announcement: who, where, altitude, heading, intentions, and then you listen. Absolutely no need to say anything else. If someone hears / sees you they tell you they do or don't have you in sight and give you the info about their whereabouts and intentions. Done it this way many times, works like a charm. As an exception, when approaching known busyish airfields, I'd sometimes ask if there is traffic there. Sometimes ppl are so preoccupied with pattern work they forget to tell they are grinding around.

The phrase "Any traffic in the area, please advise" (which is slightly different from the phrase quoted in the question) carries an implication that the pilot is not aware of any traffic in the area, and I'd suggest that in some cases it does have some usefulness.
I've used this phrase when there seemed to be no one around--almost exclusively very early in the morning, or in the middle of the night-- and my intentions were to do a whole "cloverleaf" series of touch-and-goes on an airport with a "cross" runway configuration-- e.g. depart on heading 35, climb briefly and then begin turning toward final for 09, depart 09, climb briefly and then begin turning toward final for 17, etc. I didn't explain my full intentions in advance, just announced each departure and then said "turning final for..., any traffic in the area please advise".  In this case it might have been hard for someone to figure out whether or not they were "conflicting" traffic.  I'd suggest that in this situation, the phrase "Any traffic in the area, please advise" is better than "Conflicting traffic please advise".
Obviously a pilot wouldn't be maneuvering in such a way if he/she was aware of a significant amount of traffic in the area, and he/she would wish to be aware of any traffic in the area--or at least any traffic planning to take off, land, or shoot an approach-- regardless of whether or not said traffic perceived themselves to be "conflicting".
I usually preceded such maneuvers with a brief explanatory call to the effect of "intending to shoot touch and goes on multiple runways", and then used the "any traffic in the area please advise" phrase with each new "turning final" call, or at least once every two or three such calls.  (The time interval between some of those "turning final" calls was rather short!)
In this particular case, one argument for using the "Any traffic in the area, please advise" phrase as opposed to just assuming the mere act of talking over CTAF is an implied request for conflicting traffic to speak up as needed, is that it carries a suggestion that the pilot is willing to modify his planned flight path if the planned flight path would inconvenience another pilot.  In the particular case I've described above, it seems to add an element of courtesy as well as enhancing safety.
Obviously this situation is quite different from a case where use of the phrase is likely to "get CTAF blocked for everybody" due to a large amount of traffic in the area.  But even the "any traffic in the area please advise" or "all traffic in the area please advise" phrases shouldn't be taken as a literal request for everyone within radio range to speak up.  If the request is from a pilot who is clearly operating closed circuit at a given airport, one wouldn't necessarily expect to hear answers from aircraft five or ten miles distant from that airport-- or many thousands of feet above that airport-- unless they are inbound for an approach or landing there.
The phrases "conflicting traffic please advise" or "any conflicting traffic please advise" seem awkward to me.  Both seem to put a burden on other pilots to determine whether they are conflicting with your intentions, and the first may seem to imply that you suspect there may be a conflict.  I'm having trouble thinking of a case where using one of these phrases would be better than simply announcing your position/ intentions, and listening for anyone else to respond by doing the same.


text:
How impactful could an ATC-specific speech-to-text AI model be for the aviation industry?
Various initiatives, such as the European SESAR 3 program, the Airbus Speech Recognition Challenge, or Appareo's technology, highlight a growing interest in tailored Automatic Speech Recognition (ASR) solutions for air traffic control communications.
While my knowledge is limited to projects mentioned, I wonder about the broader implications and potential beneficiaries of a successful implementation of such technology. How could air traffic controllers, pilots, or airlines find value in this specialized ASR technology?
The primary application seems evident - reducing the workload for pilots and controllers through efficient transcription. However, as an aviation newcomer, I’m curious about the additional structured information that could be gleaned from transcribing and language-processing the ATC utterances - beyond what's currently available or inferable through structured sources like ADS-B or ACARS data.

Welcome to Aviation.SE.  Are you associated with any of the sites that you linked to?

If my experience with Chat GPT is any measure, AI has a LONG way to go before it can be entrusted with peoples' lives.

@RalphJ Thanks! I'm not associated in any ways with the linked projects above. I'm mainly trying to understand if any sort of valuable piece of information could be extracted from transcribed ATC utterances - especially in non-safety critical situations. For instance, could relevant data be caught from an ATC transcription, transferred to ATM softwares, and enhance airlines' operations management ?

@JohnK Completely agree. We can't possibly allow peoples lives to be lost over some not-so-intelligent AI. AI transcripts are probably 30% incorrect.

The difference in impact between a really, really amazingly excellent model, and a fairly good model, is worlds apart. If I don't understand what was said on the radio, I can ask the sender to "say again", and that works. If the model doesn't understand & guesses wrong, all sorts of bad things can happen. If it's frequently marking *** (i.e. unintelligible) in a transcript, that becomes a nuisance & a time drain for people who can do better without the extra layer between the speaker and the hearer.
Nobody cares if a YouTube video gets a transcription error; with ATC the stakes are exponentially higher. Until the accuracy is orders of magnitude better than we've seen so far, there are scant gains and significant risks from any such models. Eventually, with everything becoming good enough that the errors from the technology are less than the errors of what we do now, we'll probably see that sort of thing being adopted. How far out that point is, however, is somewhere between an opinion and a guess.
In the meantime, datalinks are gaining adoption (i.e. CPDLC) in certain phases of flight, and Digital ATIS (i.e. computer voice reading the text aloud, saving humans time in both the reading and the copying, since it's also sent over ACARS) have brought incremental gains. Speech to Text in any ATC context is probably pretty far off down the road, in my opinion.

Would suggest the key sticking point is that a carefully ATC optimised AI will fail at the worst possible time, since an emergency will by definition involve things outside the training data set. Human pilots and ATC can be trained for emergencies by being asked 'what would you do' questions. Current AI training would instead require a massive library of synthetic emergency communications being generated and then curated/annotated by experts. AI would also need to process out of channel context - eg engine failure on a single engine aircraft vs multi engine.

I agree with this assessment, we had a training system in Australia that was meant to work based on voice. It could handle the basic commands with no issues, but when it went to anything but the most basic of commands it failed to comply. We still use people to pretend to be pilots on that simulator even though it has this capability.

I don't think is going to have a good impact implementing something like that, at least with the current technology. As others have mentioned, the risks can outweigh the benefits.
However, I do support 100% the opposite implementation of that, Text to Speech.
Not only I think the benefits would outweigh the risk, but also the suggestion of that implementation is to only use it for predefined messages so there is no guessing or any AI in the middle of the transmission.


text:
What exactly is the pressure thrust component and why does it exist?
I'm teaching PowerPlants on a ATPL theory course and honestly have some trouble wrapping my head around this one:
Most literature describes the term "pressure thrust" – as opposed to "momentum thrust" – by explaining that during high thrust conditions in a choked exhaust, the exhaust gas reaches the speed of sound and cannot be accelerated further and thus the static pressure of the gas increases beyond atmospheric pressure, this pressure thrust is added to the momentum thrust to make up the total thrust.
Firstly – it is well known that exhaust gas velocities of aircraft can easily go supersonic, take a fighter jet for example... why is this a restriction in per say turbofan engines?
Secondly – it is often emphasized in training material that you should avoid thinking of thrust as acting on / pushing on the ambient air behind the engine, as opposed to thinking in terms of Newton's 3rd law... but isn't that exactly what pressure thrust is? It's defined by pressure $\times$ the area that it is acting on...

Indeed, exhaust gases can be expanded beyond Mach 1, and doing so will result in higher thrust from higher propulsion efficiency. The problem is that pressurised gas is expanded by constricting the cross-section area when lower than M1, and expanding it when higher than M1.
So in order to achieve full expansion to ambient pressure $p_0$ at supersonic exhaust speed, we need a cross-section that narrows, then expands, for all flight circumstances. The figure below illustrates how this is done in supersonic fighter jets: with an ejector jet exhaust.

The primary exhaust is mounted inside a pipe, and the expanding exhaust gas sucks in a secondary flow, which dampens the primary flow expansion so that it takes place gradually. The secondary flow can be considered as the diverging part of the exhaust, and protects the actual metal exhaust from afterburner heat. In supersonic fighter jets both the primary and secondary exhausts are adjustable: pic left for subsonic speed, right for supersonic speed.

So full expansion is possible yet complicated, with the necessity of constantly varying exhaust nozzles.

Firstly – it is well known that exhaust gas velocities of aircraft can easily go supersonic, take a fighter jet for example... why is this a restriction in per say turbofan engines?

Because the turbofan's main flow is through the fan, which is only a compressor, no combustion takes place in this flow. In most circumstances the bypass flow is fully expanded at sub-sonic speeds - if it would not be the case, constructing in total four concentric regulated exhaust nozzles like in the pic above would be complicated and heavy, for very limited gain.  Only above M1.5 will there be a significant thrust gain from full supersonic expansion.

Secondly – it is often emphasized in training material that you should avoid thinking of thrust as acting on / pushing on the ambient air behind the engine, as opposed to thinking in terms of Newton's 3rd law... but isn't that exactly what pressure thrust is? It's defined by pressure × the area that it is acting on...

Exactly right!

considering the fans.. not only would it be heavy and cumbersome, but to actually reach sonic speed in a nozzle, you need critical pressure ratio (roughly 1.9), and that's not provided by the fans.

it's really two questions-
1) Compressible flow in ducts
The first part of the question addresses how to accelerate a flow in ducts to supersonic speeds. In simple terms, for compressible flow in a pipe with varying diameter:

when subsonic, it accelerates along the pipe, when the diameter of the pipe reduces
when supersonic, it accelerates along the pipe, when the pipe widens.

in order to produce supersonic flow, you need

a duct that first contracts, to accelerate the flow to Mach 1 at the throat,
then a duct that expands from there, because otherwise no further acceleration for the flow will take place - and it will remain at Mach 1
(super)critical pressure ratio, otherwise the flow will just accelerate to something below Mach1 in the throat, but since it's not supersonic, the divergent part will decelerate the flow again.

a bit more more in-depth, if you want: https://en.wikipedia.org/wiki/De_Laval_nozzle, or   https://en.wikipedia.org/wiki/Choked_flow
The cannot be accelerated further part refers to non-divergent nozzles. For supersonic designs, then there's a part about adapting the nozzle - meaning that the nozzle ideally should expand just enough so that the exit static pressure matches the atmospheric ambient, otherwise you get over- or under-expansion with a reduction in efficiency.
2) Momentum Conservation
Thrust does in fact consist of two parts. The idea is, that when drawing a control volume somwhere, the reaction forces on this control volume are

The reaction forces to balance to the change of momentum in the flow
the sum of all pressures on the surfaces of that control volume (or mathematically more correct, the integral of the pressure normal to the control volume surface A:  $\int_A p \vec{n} dA $ )

As a simplification, we could assume that the differences in pressures before and after the engine - far enough - are negligible, and then only the differences in momentum (stream velocity * density) provide the thrust. But if the pressure differences are large enough, this cannot be neglected any more.

The mathematical formulation gets a bit involved, then... but you can see the pressure terms.
https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node78.html


text:
How would flying into Frankfurt a.M. Airport be problematic for the Tu-154?
A friend of the family lives in the approach path of Frankfurt a.M. Airport (FRA, EDDF). Until a few years ago, Tupolev Tu-154s were still flying to this airport, although as I understand, they don't anymore due to noise issues. I could not find out when exactly the last Tu-154 flew to Frankfurt, but the newest photos on Wikimedia Commons are from 2012.
The friend told us that the Tupolevs flying over his town always looked like they were about to fall out of the sky the next minute, because they were somehow flying in an aerodynamically unfavourable configuration, probably due to the aforementioned noise issues.
I find this hard to believe, since from what I have read, the Tu-154 should be more aerodynamically "forgiving" than other planes. For example, to compare the newest variant, the Tu-154M, with a Boeing 737 MAX:

Tu-154
Boeing 737 MAX

wing area
202 m²
127 m²

maximum takeoff weight (MTOW)
104 t
89 t

thrust
103 kN * 3 = 309 kN
130 kN * 2 = 260 kN

Source Tupolev-154 Source 737 MAX
Now the MTOW of the Tupolev is a bit higher than the 737, but with that much thrust and wing area it should generate more lift than the 737. The Wikipedia page also states the Tu-154 was designed for short runways and harsh conditions. That plane can land on a 700 m runway. All this considered it should be able to fly into a nice big-city airport easily.
Unless however the thrust was limited (e.g. for noise reduction).
So now I'm wondering:
Would regulatory or technical conditions force the Tu-154 to fly in an unfavourable or unusual configuration when flying into Frankfurt? Or is our friend wrong?
Information or experiences from other airports and other countries are also welcome.
I have found a video of a Tu-154 landing at Frankfurt, but it only shows the "last few meters" and does not look unusual to me:

See page 10, the noise fees (NEF) are the highest for Tu-154, 4x the B737-800

I'm no expert, but that looked like a pretty nice and "normal" landing to me.

Your friend is wrong.
The Tu-154 is one of the safest Soviet designs and certainly was not about to fall out of the sky when departing Frankfurt. However, it is indeed a noisy airplane and in order to minimize its noise impact would try to climb more steeply. The flight speeds for steepest climb is only three quarters of the speed for best climb, so it might seem that the Tupolev was flying more slowly when compared to more modern types with larger bypass ratio engines. This might look to the untrained eye like a stall being imminent, but that impression is plain wrong.
During approach the engines would run near idle speed, so noise would be less important. Now I have to speculate what made the Tu-154 look so different. Its large wing area and large flaps give it a very low approach and landing speed - might it be that also during approach your friend judged the airplane to be too slow?

And it was also a pretty comfortable ride (apart from the noise, but that wasn't too different from contemporary western aircraft like the 727 or Trident). Overall not a bad aircraft at all, and had it not been for the east-west rivalry may well have been much more successful on the international market.

Also its engine bay free pure wings are more performant than engine mounted wings. This certainly help with better tolerance to low speed.

This, and in addition they probably also performed steeper descents than standard 3° for the same reasons.

So it performs a similar takeoff as jets do at John Wayne Airport (KSNA)?

I would be surprised if they flew anything but a standard 3° approach path. The airspace is complicated enough already with everyone on standards, isn't t?

I believe the Q implies approach/landing, not climb. Tu-154 approaches with about 80% N2, which is about 50% thrust. Generally, most airplanes are quite far from idle in the landing configuration. Tu-154 is also not particularly slow: 240-275 km/h for typical weights vs 130-140 kt (240-260 km/h) for 737-700. I suspect this is just perception: unusual shape, noisier 'whining' smoky engines, etc.

@Zeus I covered both, departure and landing. It seems you know more about the Tu-154 than me - care to write an answer yourself? I share your suspicion, there is no rational reason why it should look so differently.

@Peter, but that's the thing: it likely has nothing to do with Tupolev's specs. The rest is covered already. Actually, busdriver had a plausible idea, but I have no information if such things were in place. (I know that normally Tu-154 had only one landing flaps position, and lower settings were approved for engine(s) off landings). This would increase approach speed by 15-20 km/h though...

Given the speculative nature of this question I dare to speculate myself :)
With DC-9s part of the solution to reduce noise during approach was to ban use of full flaps. This was done to reduce drag which in turn reduces required engine power and noise.
The result of lower flap setting is that higher nose-up attitude is required. If similar procedure was applied to Tu-154s, with its large wing sweep angle, it can give an impression of very high nose-up attitude when looking from below.

Sounds very credible. +1

That sounds reasonable. If anyone can produce a media report or, even better, technical guideline of some sort, I will accept this answer.


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Do stealth plane need to turn off its radar to remain in stealth?
If yes, the radar needs to be off, how can it detect enemy plane, locked-one and fire missles?
If stealth plane still operates its radar, can enemy planes detect its radar emission and pinpoint it location instead?

That (duplicated) question is a pretty awful question, but the answers to it are good, and they do address this question pretty well. VTC as dupe.

Yes, having your radar on will make you VERY detectable.
Think of two guys walking around a dark warehouse, light off. Both have a pistol and a flashlight. Whoever turns their flashlight on first loses.
So what do the stealth pilots do? In a competent Air Force, they have an AWACS orbiting 75 miles away, telling you exactly where the bad guys are. If the AWACS can get me to within 25 miles (later models much farther) and pointed in mostly the right direction, I can fire an AIM-120, and lets its own radar take over. The radar in my aircraft never needs to be turned on.
But later....
If we're just 1 v 1 or 2 v 2, 'stealth' is not meant to make you "invisible", just harder to detect. If the better stealth on my jet gives me a 1 minute advantage in detection over your jet, you lose.

So how does this work? If the other craft is transmitting known data at a known frequency it should be easy to determine its position using multiple antennas. You just measure when the data arrives at the antennas and use the small time difference in arrival time to calculate its position. But I can’t get my head around how you’d do it for an unknown signal which is only transmitted in pulses and directionally.

@Michael antennae are typically not super targeted at one frequency, and radar isn’t going to diverge much.

@Michael Ultra-wideband receivers. UWB radio existed since the original invention of spark-gap radio (that's what spark gaps are: they transmit pulses on almost all frequencies) however processing the signal was impractical until the invention of software-defined-radio. With SDR you don't need tons of decoders and demodulators and filters to process multiple frequencies. You can do all that in software. To process more frequencies in parallel all you need is more CPU power.

Receiving the signal seems straightforward, but what I’d like to understand is how you filter it out from all the other (maybe even deliberate) noise and determine its time of arrival. Especially if you are not just interested in the strongest signal (where calculating a cross correlation might be sufficient).

A notable mention is that some (Russian) planes use IR detectors to detect aircraft (-exhausts) in-front of them. This is notorious because you will only receive (in the most hopeful scenario) a missile launch warning when the IR-seeking missile is launched.
Like this IR tracker on a SU-35:

https://en.wikipedia.org/wiki/Infrared_search_and_track

Aircraft can (and almost certainly do) use passive radar. This uses a third-party emitter, often a TV or Radio mast.
The radar system, by observing the direct signal from the mast, and the echos from other aircraft, determine their range and direction. By using Doppler corroboration, the speed of the target towards/away from the receiver can be determined. After observing the target for a while its current heading can be calculated.
A phased antenna array allows the direction a signal came in to be determined, without moving the antennae.


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How is the wing's longitudinal position determined?
What I mean is, for example the MD 80 aircraft have a wing placed way back near the engine why not put it on the center? but the Boeing 737 have a centered wing. I'm asking this because I love to make cardboard planes but I don't know where the best spot to place the wing, I've put the wing on the front the middle and at the back but I still don't know whats the different. anyone got answer.

The position of the wing is determined by many things, but primary among them is an  analysis of the distribution of the weight of the aircraft. Aircraft remain stable in flight because there is a balance of moments (that is, the nose up/nose down rotational effects of the forces generated by the airflow over every part of the aircraft). The total moment generated by all the aerodynamic forces on the surface of the aircraft will cause the nose to pitch up, or pitch down, depending on where the total force vector from all these forces lies in relation to the center of mass of the aircraft (often referred to as Center of Gravity or CG). All moments rotate the aircraft around the CG. It's just like a balance beam, or a scale with sliding weights, except that instead of having a fixed point that everything rotates around, the rotation point is the center of Mass. If you move the sliding weight on a scale to the right, the beam rotates down on the right, until an equilibrium is reached. The same thing happens with aircraft. If everyone in an aircraft moves to the front, or if cargo shifts forward on a transport aircraft, the aircraft will pitch nose down due to the change in the position of the CG. The aircraft's pitch attitude is only stable when the total aerodynamic force vector passes directly through the CG.
(Bear in mind that this is a complex dynamic thing, if the vector is not aligned with the CG, and causes a pitch change, the change itself will also cause a change in the position and strength of the aerodynamic forces. For the aircraft to be stable, these changes should bring the force more closely into alignment with the CG, rather than further away)
So, to answer your question, the wings are near the middle on a 737, and nearer to the tail on a MD-80/DC-9, because that's where the CG is. With the exception of the engines, and fuel, the weight of an airliner is pretty evenly distributed from front to back. The engines and fuel comprise a significant percentage of the total weight. So The CG on a 737 is near the middle because that's where the engines are (slightly forward of leading edge of the wings). And the MD-80/DC-9s engines are mounted at the back on the sides of the tail section.
On your paper airplane, first determine where the CG is. Balance the aircraft of the edge of a ruler, or hang it from a thread. Then place the wing so that the point one quarter of the way from the leading edge to the trailing edge is slightly behind the CG. Adjust forward or backwards from there until it flies the way you want. (Alternatively, you can add or remove paper (weight) from the nose or tail of the airplane to create the same effect.)

Without entering into details of aerodynamics:

The weight of the aircraft must be balanced by lift so altitude can be maintained constant. Lift can also be increased or decreased to climb or descend.

For many problems, weight can be seen as acting at the center of gravity, even if weight isn't actually a single force acting at a single point.

For the same reasons lift can be seen as a force acting at the aerodynamic center (AC, also named center of lift), even if the aerodynamic forces occur at any point of the wing and other lifting surfaces.

As CG and AC are not coincident, a nose-down moment exists.

To cancel this undesirable moment, an opposite moment must be created with the horizontal stabilizer.

The size of the horizontal stabilizer and the distance to the CG produce the desired moment. Varying this moment with the elevators changes the pitch attitude.

The tail also creates drag, depending on its size and the amount of lift generated.

Aircraft designers take all these elements to create a safe stable structure, easily flyable, including with engines shutdown. The total drag must be limited as much as possible to use as less fuel as possible. This leads to different choices and different relative positions for CG and AC.
For the MD-80, engines are closer to the tail, moving CG location more aft than when the engines are under the wings. The AC-CG distance is increased, so the pitching moment created by the wing is also increased. To compensate, the wing is moved backward.
The horizontal surfaces of the tail are in a T-configuration, which is weaker than a regular low configuration. It's desirable to limit the force generated by the tail. Such constraint and many other similar ones play a role in determining the exact location of AC relatively to CG.

Your diagrams are not correct. In conventional aircraft, CM(CG) is ahead of AC not behind. The tail generates download, not lift, to balance. CM ahead of AC is stable, the converse is not. If the aircraft stops flying for whatever reason, CM ahead of AC helps get the nose down to assist in recovery.


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Why is there an intake in front of the landing gear on this C-160?
I went to a aircraft museum and saw this C-160, it has intake in front of the landing gear which is now blocked with the orange thing as you can see below in the picture below. Why is there an intake right in front of the landing gear, what purpose does it serve?

Inlet only on the right side.

@mins There is an inlet on the left side too, smaller and square shaped, for the apu located in the front of the left sponson.

It's the intake for the air conditioning system.
Source (last post on the page by "antonkr":

The round hole on the leading edge of the starboard sponson is the intake for the very well-designed and super-efficient Air Conditioning System. This system was run via the APU whilst the aircraft was on the ground. It worked so well that many passengers, specifically those that were seated on the starboard side, were startled when chunks of ice rattled in the pipes. Whilst the system was running at full blast, vapour formed inside the cargo hold, even with the ramp and door open. At a place like Ondangua in high summer, this was magic!


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Why is the turbine that drives the compressor is placed before the free turbine in a gas turbine engine?
For example in the picture below we can see that the turbine of the compressor is just behind the combustion chamber and gets the hottest gas and i think therefore can extract the most energy? The power turbine comes after the compressor turbine but power turbine is the turbine that propels the vehicle. Why is the power turbine placed after compressor turbine if it is the one propelling the vehicle, shouldn't it be placed first so that it gets the hottest gas and extracts the most energy and propels the vehicle forward with more torque?

But-- if you did that, you'd be taking energy away from the turbine that keeps the motor/engine turning in the first place!  This seems kind of like a "if I do this, can I get closer to having perpetual motion" kind of question.

The compressor-turbine spool, the "gas generator" in turboprop/turboshaft lingo, or "core engine", in a turbofan, has to come ahead of the power turbine because the turbine has to be directly connected to its compressor to maintain the combustion cycle.
The power turbine needs to go after, its shaft either running inside the spool of the gas generator out the front, or out the other way (like a PT-6, similar to your diagram).
To put the power turbine ahead of the compressor turbine, you'd have to transmit its power through some transmission method at the outer rim of the turbine, maybe using a ring gear on the outside of the power turbine.
Aside from flow issues likely to have to be overcome when you are extracting energy ahead of the compressor turbine, you would have an unwieldy transmission structure on the outside of the engine, where a pinion gear would mesh with the outside of the power turbine. Just thinking about it sounds like a mechanical nightmare.
So much easier to stick the power turbine in the exhaust of the gas generator, like putting a windmill behind a regular turbojet's exhaust.
In any case, the energy required to compress the incoming flow has priority over energy being used to make torque, so that's another reason to put the power turbine after.

i see thanks, also im wondering one more thing. You said that "the energy required to compress the incoming flow has priority over energy being used to make torque", do you know in a general gas turbine engine, roughly how much percentage of the power is used to drive the compressor and how much percentage is left to drive the power turbine?

Not off the top of my head, and I'm retired so I can't ask anybody to find out any more lol.

The "compressor turbine" is the turbine (or group of turbines) which extract from the exhaust enough energy to drive the compressor stages, nothing more.
The remaining energy possessed by the exhaust after the "compressor turbine" can be used in two ways:

we add another turbine (called "free power turbine") which we connect to the propeller (in a propeller airplane) or to the rotor (in a helicopter) or to an electrical engine/generator (for ground applications); in total some 80% of the energy is converted in torque on the shaft;

if the jet engine is used to push (thrust) the aircraft then no "free power turbine" is needed and the whole exhaust energy goes into "pushing" the airplane.


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Why are aircraft piston engines are so low rpm lazy engines?
I understand that the propeller speed should not be too much otherwise it will stall at the tip and be useless so higher rpm engine would be useless when we first think about it. However, we can put a single speed gearbox between the crankshaft and the propeller to reduce the speed of the propeller so that it will not stall at the tips. We can have an engine running at 6000 rpm making lots of power and through a 6:1 reduction gearbox the propeller will rotate at 1000 rpm and im guessing at that rpm the propeller tips wont stall. Why is this not done? Why are the aircraft engines so lazy low rpm engines with low power output? For example the 5 Liter GO-300 engine  makes a peak power of 175hp at 3200 rpm , what would be the downsides of putting a 4 Liter Porsche 911 GT3 flat 6 engine that makes 500hp at 8500 rpm and then through a reduction gearbox decrease the speed of the propeller so that the propeller tip wont stall? Also im giving the porsche engine as an example because that engine is also used in 24 hour races constantly and they are extremely reliable.

Running an engine for 24 hours isn't "extremely reliable" at all. An ordinary car engine goes for 5,000-7,500 hours without any internal maintenance. And then, when people's car engine stop, you normally don't have a crash or fatality.

@user71659 These engines generally require full rebuild after around 100 hours not 24. The regular car engine you are talking about that lasts 7500 hours pretty much never sees the redline in its entire life. It makes no sense to compare a regular car engine that realistically never goes above 3000 rpm to this engine to say "its not reliable". This engine is constantly abused to extreme levels in that 100 hour interval. But yes now looking at O-300 it says interval is at 1200hr , so i guess reason why a high rpm high hp engine is not used is due to much more frequent rebuild interval and cost.

Low RPM is good b/c it means less friction generated heat.  Engine life is largely a function of distance traveled by the piston rings. Low RPM means more flying time for a given distance of piston ring travel.  You want direct drive for the reasons Jan gives in his answer, and that means you generally relay on displacement, and get 1/2 hp per cubic inch in order to achieve a torque peak under 3000 rpm. An aircraft engine's environment is closer to an industrial engine.

To add on to @JohnK the idea of small-displacement high-revving engines comes in a large part from obsolete European and Asian car taxes based on pure displacement. There have been examples of car engines brought to the US are modified to be slower and larger, and save fuel. Viscous drag from engine oil and moving parts scales to the square of velocity. As mentioned, it also affects wear, which is also compounded by the use of lighter oils to compensate for high speeds, but is hidden by European vehicles driving significantly less per year than the US.

You absolutely can put a Porsche 911 motor in a plane and it will absolutely make a terrible plane

There are really only three automotive based aircraft engines with a modest record of success; the VW Beetle engine, the Subaru EJ-22 4 cyl, and, wait for it... the Corvair. The Sub requires a reduction drive, but the core engine as an opposed design with cast-in-one-piece case and barrels, is extremely rigid and it seems to be able to handle extended high stress. The Corvair works very well direct drive, up to 3000 rpm where it will make close to 100 hp, when an extra support bearing is added for the propeller. Similar for the VW, although it has to spin up faster & uses smallish propellers.

@Dave Those links are nice thanks for sharing.

A reduction gearbox is a non-trivial piece of fine machinery that needs to be maintained and can fail. And since reliability and low maintenance cost are important design goals for aircraft engines, especially engines for small aircraft, it makes sense to design the engine without need for a gearbox and just accept the need for a bigger cylinder volume for the same power.
But the newer deigns, like the Rotax or Austro Engines ones, all do have reduction gearbox. These designs are derived from automotive designs and those generally run at slightly higher speeds.
Note that the difference isn't that huge. Typical small aircraft propellers have maximum RPM 2,700, with maybe 2,400 RPM being usual cruise setting, and the automotive engines don't normally go over 4,500 RPM, with 3,000–4,000 being typical cruise speeds.
The main obstacle to newer engine designs for aircraft is the certification. While the engines themselves are pretty reliable these days, they are all electronically controlled these days and that adds failure points that all need to be carefully validated, and backup sources of electric power need to be provided and such, which is a huge effort. So instead a lot of light aircraft still use the older tried and tested simpler ungeared engines.
Side note: the tips of a propeller won't stall by spinning faster. Rather they will generate more drag, wasting power, and once the tips go supersonic (close enough to supersonic to start causing shock waves to form), vastly more drag, wasting even more power.

There's also torsional resonance issues, the bigg bugaboo for geared engines with few cylinders.  Molt Talyor, for his flying car that he certified in the early 50s using a Lyc O-320, used Flexidyne dry fluid couplings used in washing machines etc, a housing with a wavy plate filled with ball bearings, to provide the compliance in the  drive line to absorb resonant pulses. Rotax relies on rubber couplings and/or slip clutches, and careful tuning of the system.

Why are aircraft piston engines so low rpm?

The fuel consumption of a typical aeronautical piston engine depends, all the rest being equal, only on the rotating speed rpm with a typical bell-shaped curve (source):

As visible in the previous plot, there's a range of rpm (more or less from 3'000 to 5'000) where the fuel consumption is minimised. The design goal of a gearbox is to supply the propeller with the needed rotating speed so that the engine's rpm remain inside that optimal range. This minimise not only the fuel consumption but also the engine's wear. Making the engine run at a higher rpm simply consumes more fuel plus requires a bigger and heavier gearbox.

I understand that the propeller speed should not be too much otherwise it will stall at the tip.

The limiting factor is the onset of transonic speeds on the tip which greatly increases aerodynamic drag and therefore the needed torque.


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How to input Reynolds number and Mach number as input boundary conditions in Ansys Fluent
I am trying to validate the pressure distribution and drag polars of some basic aerofoils using Ansys Fluent however the only conditions given are the freestream Mach number (0.735) and Reynolds number (6000000). I am modelling the external flow around the aerofoil in Ansys and therefore am trying to resolve this in a way that can be input into Ansys, for example would it be most appropriate to use intensity and hydraulic diameter and how so?

Voting to keep the question open, it is about aircraft aerodynamics and has attracted a good answer

I’m voting to close this question because it is asking for product support, not for aerodynamics insight. and the only answer it got says (paraphrasing) "I don't know about this numerical solution, you just need to solve the Navier-Stokes equations" that is definitely NOT what OP asked about.

Disclaimer: I am not familiar with ANSYS, so this is just plain physics.
You need three parameters to describe flow conditions:

air speed
air density at rest
air temperature at rest

then all other parameters can be determined from those three. Take air pressure for example: It is density times temperature and a constant which for air is $R$ = 287.085 J/kg·K.
To arrive at the desired Mach number, you need to know the speed of sound at the given atmospheric conditions. So you need to determine a temperature $T$; once you have this, the rest is straightforward:
$$\text{speed of sound  }a = \sqrt{\kappa\cdot R\cdot T}$$
$\kappa$ is the ratio of specific heats and for a diatomic gas at room temperature is 1.405. So lets pick 20°C (which makes $T$ = 293.15K) and plug in the numbers: $a^2$ = 1.405·287.085·293.15 = 118,243 and $a$ = 343.8 m/s. For Mach 0.735 your flow speed at infinity must be 252.471 m/s.
The Reynolds number now gives you the size of your airfoil. When we know the gas (air) and the temperature, we can look up the kinematic viscosity $\nu$ = 0.0000156 m²/s. Now, with Re = 6,000,000 given, we can solve for the length $l$: $l$ = 0.0000156·6,000,000 / 252.471 = 0.37 m. That should be the chord length of your airfoil to hit the desired Reynolds number.
For different temperatures or gasses you only need to use other numbers, but the process is the same.

Strange - I correct a glaring mistake in the answer and get an unexplained downvote as a consequence. Should I leave flawed answers stand?


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How does a towed banner maintain a steady tilt?
Today a small airplane is towing an advertising banner, about 20 by 30 feet, in a circular path around my town's university campus.  The banner stays tilted about 45 degrees to make it easier to read by those whom the airplane is circling.  Winds are 10 knots gusting to 20, if that matters.
How can it maintain that tilt?  Surely the tether can't exert a torque on the banner.
Websites of companies such as Van Wagner Aerial Media and Airplane Banners Nationwide say they can do this, but without explanation:

Each advertisement will be tilted, with your choice between zero and 90 degrees, towards your audience.

Banners have a lead pole to keep the leading edge straight. This pole is weighted at the bottom, which ensures that the top and bottom of the banner remain in the correct place.
By itself, this would ensure the banner remain perfectly vertical. To achieve the proper angle for viewing on the ground, a tab is attached to the top of the lead pole, adjusted to the required angle to push the top of the pole in the desired direction to achieve the right viewing angle.
Here's a quick sketch to try to illustrate the setup, with the banner, pole, weight, trim tab, and harness:

Here, we're looking at about a 45 degree angle from ahead of the banner, with the trim tab adjusted to the left of the banner's direction of flight, causing the top of the banner to tilt to its right:

In other words, the tab at the top of the pole acts similarly to an airplane's rudder, where deflection to one side results in a force applied in the opposite direction.
More reading here:
Aviation Stack Exchange: How are banners kept upright?
Pilots of America: Banner aerodynamics
Quora: How are flying banners stabilized?

I had envisioned this earlier before you posted the picture and thought, 'that wouldn't work because then the constant pressure on the tab would keep the banner rotating." But I didn't envision the weight at the bottom. The tab provides enough pressure on the top to tilt the lead pole, but not enough to overcome the weight at the bottom. Thanks for the drawing!


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How was the AeroVironment Helios able to fly to the edge of space at no more than 23.5 kn?
The NASA/AeroVironment Helios holds the FAI record for the highest sustained horizontal flight at 96,900 ft (29.5 km) MSL. It reportedly spent more than 40 min above 96,000 ft. It could fly no faster than 23.5 knots, hence those records are extremely hard to believe. What is its stall speed? How could it fly that high on two-blade-propellers? Could it carry a human who'd lay on its middle into the stratosphere?
And since the Helios, the Pathfinder and the Centurion were meant to be test atmosats, are there any images from the edge of space by them? I couldn't find any.

By god how many Giovannis we have here?

@Jpe61 All Giovannis are the same person, except for the user Robert DiGiovanni who's a different user.

@mins But that's a glider. Did the Helios use lifts gliders use as well, such as wave lift?

User page states "member for 2 days", that does not compute. As for the speed, why is it not plausible?

@Jpe61 Because when I ask a question on another SE site, and on aviation again, I'd have a new account here. The speed doesn't sound plausible because aircraft stall at much higher speeds, even near sea level. Hence my question what's different for the Helios than for other planes?

Ok, I understand the premise of the question now.

You do realize you can use same SE account on all SE sites? No need to create new accounts?

@Jpe61 The new account is being created automatically, by posting a question or answer in another SE.

In case you haven't been keeping up with the space news, NASA is currently flying a helicopter on Mars, where the pressure altitude is 100K ft or more: https://mars.nasa.gov/technology/helicopter/#Quick-Facts

@jamesqf Yes but that's a helicopter/drone, it rarely has any horizontal speed, Ingenuity mostly flies vertically. I'm talking about planes. Airplanes need to fly somewhat horizontally to fly (up), unless they have hover engines like the Harrier. The atmosphere of Mars is denser btw because it's carbon dioxide which is denser than the Earth's air composition.

@mins I wrote edge of space on purpose, but the 100-km-boundary is wrong (it's not "the" Kármán line) and exaggerately high anyway. There's no abrupt border between the atmosphere and the vacuum of space, you have to define one. You may define it at a layer border such as the stratopause. At 30 km (100k ft) the sky is pitch black and you see the brightest stars and the Earth's curvature. When I.C. Kincheloe flew to 126k ft in the X-2 in 1956 he was declared the first man in space.

@Giovanni: Space density limit is indeed a convention and varies according to the needs, 100 km for the limit of wing lift generation and balloon buoyancy, and 122 kilometers for spacecraft reentry interface. So at 80 km, lift generation is still possible, at 140 it's not. At 30 km, or when you're flying, you're nowhere in space according to conventions.

@mins Balloons can't fly higher than ~60 km (200k ft). Wing lift generation (and therefore the Kármán line) depends on the mass and density of the planet in question, not just the atmosphere, so it cannot be universal. For Earth the average value is 83.6 km above sea level. The Helios reached 29.5 km and no non-rocket plane flew higher in sustained horizontal flight (unless you count the X-43 which flew at 33.5 km).

@Giovanni: The blades on a helicopter rotor are airfoils, just like wings and propellor blades.  And while CO2 is somewhat denser than Earth's mostly N2 & O2 mix, it's not dense enough to offset the fact that there's only about 1% as much of it.

@jamesqf Well, but it are rotating airfoils and they're four blades, the Helios has two blades each. Additionally, Mars' gravity is 3/8 that of Earth's.

@mins BBC considers the U2 at 70,000 ft flying at the edge of space, and the pilot does so too: https://www.bbc.com/future/article/20140224-flying-at-the-edge-of-space

"BBC considers the U2 at 70,000 ft flying at the edge of space, and the pilot does so too". That's good news for future low altitude space stations.

@mins You mean stratospheric balloons/airships which offer accomodation (say a large version of Space Perspective's Neptune)?

My answer will be a simplified one, someone with more theoretical wisdom and keyboard can expound (tapping on phone screen does not encourage long answers with fancy formatting).
All my data is retrieved from Wikipedia site.
There is nothing strange in Helios HP01's flight regime, in speed nor altitude.
The speed range is mentioned to be 16.5–23.5 kts. Stall speed is not specified.
The reasons for slow operating speed is the selected wing profile that is optimized for slow speeds, and extremely low wing loading. HP01 weighs less than 1000kg, and has wing area of about 180 square meters. This gives a wing loading of less than  5.5 kg/m2. That's roughly an order of magnitude smaller than what gliders typically have (~50), and two orders of magnitude smaller than what transport aircraft may have (~500).
So the wing has very little work to do when carrying the plane. This enables extremely slow flight.
As for the high altitude: stall speed in indicated airspeed does not change with altitude, although all kinds of other weirdish stuff does emerge as air gets really thin. That would, however be a whole can of worms in itself, and it has been opened here in many questions before. For example while indicated airspeed at 96000 ft would remain the same, keeping the plane above stall speed, the true airspeed would have increased significantly, about 20-fold, taking the plane into it's coffin corner.

Well, I'm curious on the plane's stall speed and coffin corner. And if it's that easy to fly that slow that high I wonder why don't more planes do this, and to what altitude a human lying on the Helios (on its middle) could be transported.

@Giovanni: Why would anyone want to do that?  Either you have a government program paying for research, as with Helios (see your link :-)), or you are a rich person looking to get into record books, like the Perlan glider, or the people who do ultra high skydives.

@jamesqf I would do it to fly to the edge of space.

I'm with Giovanni on that one, I'd do it too

As to the coffin corner, around FL400 or so the temp, thus the SOS stops going down, then goes back up. According to a calculator I found online, at 96,000 ft 23.5 kts yields a TAS of 180 kts and Mach .309. I don’t think Mach number was a factor. :)

@Giovanni: So you're a rich person willing to pay a lot of money for the experience :-)

@Giovanni you did ask many things in one question which is not proper way to do it  here, but I can try and extend my answer a bit later.


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What is Tendency of RVR?
What does tendency of RVR (Runway Visual Range) mean and why down and up have the same values?

This is from AWOS(Automated Weather Observing System)

that same value for up and down must be a typo!

can you provide a link to the document you extracted the table from?

When included as part of the RVR, the tendency indicates whether it is trending up (improving), down (deteriorating) or there is no change. It is usually indicated by the suffix U or D.
When reported in a METAR it means that in the 10 minutes preceeding the observation, the mean RVR in the first 5 minutes varied from the mean RVR is the second 5 minutes by 100m or more.
An example would be R12/P1200U

Runway 12
Greater than 1200m
Improving

Thanks @mins I was really struggling to find something that matched my knowledge

Thank you for your answer. Considering Metar, you're right. The message type in my case is awos not metar. So if the tendency value is 1 it means a tendecy exists, if 0 it means a tendency doesn't exist.

Better reference in ICAO Doc 9328: Table 11-2.   Detailed structure of RVR information included in METAR and SPECI.

@mins that's the one I found, but as it was Chinese I wasnt sure it was a very good (ICAO) reference.


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What does "half of the horizon circle" means?
The definition of Prevailing Visibility is:

"Prevailing visibility is the horizontal distance over which objects or bright lights can be seen and identified over at least half of the horizon circle."

My question is simple: What does "half of the horizon circle" means?

Definition
From WMO Technical Regulations, volume II, Meteorological Service for International Air Navigation:

Prevailing visibility. The greatest visibility value, observed in accordance with the definition of “visibility”, which is reached within at least half the horizon circle or within at least half of the surface of the aerodrome. These areas could comprise contiguous or non-contiguous sectors.

Note: This value may be assessed by human observation and/or instrumented systems. When instruments are installed, they are used to obtain the best estimate of the prevailing visibility.

Explanation
For someone standing on the ground, the horizon is the limit between sky and ground, and when the ground is "flat", is a circle which the person is the center.

objects or bright lights can be seen and identified over at least half of the horizon circle.

Half of the horizon circle means 180°. So visibility is the distance objects can be seen at least on 180°. This angle has not to be in a single sector, this can be 3 sectors of 60°, 20 sectors of 9° or any other combination.


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Who can access the FAA's Electronic Document Retrieval System?
I've used The FAA Aircraft Registration website to request aircraft records, which includes registraion records and forms 337.
I am now working on an airworthiness certificate for an import.  I received a checklist from the DAR, which includes the instruction "Download and review FAA EDRS files, 337s & STC's"
I've found the EDRS website, but it appears to require a login, and it is not obvious to me how I might create an account.  I suspect access to this site may be limited to FAA employees and designees.
I suspect what I need to do is to contact a DAR and ask them to pull the records on my behalf.  Am I on the right track here?  Are there others with access to this information?

I was able to get an answer from the DAR that I've been working with.  He informed me that the information retrievable by this system is the same as what is available from the aircraft registration office.


text:
Ways to find a practice area
I am taking a check-ride at an unfamiliar airport.  How should I look for a practice area for maneuvers?

Ask a local. You really should familiarize yourself with the area before your check ride. It's stressful enough without adding unfamiliarity to the mix.

If you're doing a checkride (one assumes with an instructor) won't they show you the practice area(s) they typically use?


text:
How should a newly minted instructor sign an endorsement?
A newly issued flight instructor certificate often has the word "PENDING" in the certificate number field.
In 8900.1 Flight Standards, Volume 5, Section 1, Section 5, Paragraph 5-112(c)(2)(a) Instructions are given that the temporary airman certificate for a flight instructor should be filled in with the corresponding airman certificate number with "CFI" appended.
In the event that does not happen, and the certificate number shows "PENDING", how should the instructor format their signature to make an endorsement prior to the issuance of a permanent replacement?

I would still use your pilot certificate number and add CFI to the end.  It will be the same unless you are also removing your SSN number as your pilot certificate number.  The purpose 8s there is an accident or incident with your student the FAA can know who the CFI is.  Using your pilot certificate number accomplishes that goal.

I spoke with an inspector at the SLC FSDO.  The inspector on the line told me to use my pilot certificate number with "CFI" appended, stating further that she had never seen an instance of that number not being issued.  The DPE was much more cautious.

I would think the newly minted CFI should use the same words the FAA uses: "Pending". Can't go wrong with that.

Actually you can go wrong... For example my complex rating was initially done when I had my paper license while waiting on the FAA to issue my plastic one. The CFI wrote "pending" on my logbook endorsement and it is very much invalid. I asked another CFI to fix it (because my original CFI took a job at an airline) and they wouldn't touch it without going through the training again.

That one CFI refused to accept it out of what is most likely ignorance doesn't mean he was right or that the endorsement is invalid. If it has the name of the CFI you can look it up on the FAA airman database, and the FSDO is the last word, not some random CFI. :)


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What challenges may be foreseen to adapting the Wittman Tailwind as an E-LSA?
The Wittman Tailwind is a great performing aircraft which can be built on a budget.  Many potential builders have considered adapting the design as a light sport aircraft.  What challenges could be expected in getting this design to meet the LSA requirements?

This question has been asked numerous times in a traditional format.  I posted this question to illustrate the effectiveness of aviation stack exchange to users of the forum for exchanging technical information.


text:
Why aren't requirements to use GNSS systems in the Regulations?
I've been sorting through the publications outlining the proper use of GPS in IFR scenarios.  Looking at AIM 1-2-3 (dated 10/12/17), it appears that there is some regulatory language in (b) and (c).  To me it seems this information belongs in Part 91 somewhere between 91.167 and 91.299, along with VOR checks, ELT's and ADS-B.

Why isn't this information in the regulations rather than in the AIM?

See Also AIM 1-1-17

I should also note that the FAA publications I am looking at are citing GPS specifically rather than GPS.  I presume that is because the FAA has no stake in non-US GNSS systems.

There are formal rules required to make new federal regulations and it would be incredibly difficult and time-consuming to put every detailed point through committees, public feedback etc. (Some people might actually see that as a good thing, but that's a discussion for another site.)
As for your specific example, 14 CFR 1.1 defines "suitable RNAV system" as (emphasis mine):

an RNAV system that meets the required performance established for a type of operation, e.g. IFR; and is suitable for operation over the route to be flown in terms of any performance criteria (including accuracy) established by the air navigation service provider for certain routes (e.g. oceanic, ATS routes, and IAPs). An RNAV system's suitability is dependent upon the availability of ground and/or satellite navigation aids that are needed to meet any route performance criteria that may be prescribed in route specifications to navigate the aircraft along the route to be flown. Information on suitable RNAV systems is published in FAA guidance material.

In other words, "there's far too much detail here to make this a regulation, and technology keeps changing anyway. So just go read our dedicated documentation on it".

The key words are in the first line of your quote; "system that meets the required performance". The FAA has approved standards (RTCA DO-236 and DO-283) that specify the required nav performance of RNAV systems. The FAA is rightly concerned with performance, not the means by which the performance is attained. In other words, the rules cover what the system must do, not how it does it.


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Why would the digits fade out and blink in darkness on a KX-155?
I have a radio installation with two KX-155 Nav-Comms.  These radios are equipped with a photocell to automatically dim the displays to match cabin lighting.  In dark lighting, the digits fade to the point of unreadability, with some segments being visible and some not.  I can brighten and read the displays by aiming a flashlight into the photocells.
It seems like there is a bias set incorrectly or an excitation voltage which is wrong.
Why might this be happening?

Yes, there is a trim pot on the display circuit board that adjusts the dimmer level.
The display intensity pot is R438. The red arrow points to it:

The dimmer pre-set should be marked on the outside cover, and is adjustable without removing the covers, but it only adjusts the max brightness.
It could also be the photo cell that is bad or dirty. When the display starts to loose it's brightness, that's usually a sign that it's about to go south. It can be readjusted with the pot a couple of times, then is only visible when the radio has warmed up, then finito. Try a new photocell, very easy to replace.
Be sure to observe all regulations concerning avionics maintenance!!
Source of info: http://www.337skymaster.com/messages/showthread.php?t=478

The fact that the segments aren't dimming equally indicates that the gas is starting to leak out of some of the segments. When enough leaks out the display will fail and you will need a new display. But since a KX-155 is at least 25 years old, it may be time for new radios.

The content in this answer seems to be curated from thread, which I found after posting my question: http://www.337skymaster.com/messages/showthread.php?t=478  I suggest editing for attribution.

done as requested


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Do TFRs ever have lower altitudes that are not the ground
I am working on using the FAA TFR list to restrict drone flights and all of the entries I have examined have an "Airspace Definition" that reads like "Altitude: From the surface up to and including 17999 feet MSL."  Presumably, aircraft can fly over such a TFR at 18,000 feet and above.
My question is are there ever TFRs that aircraft can fly under? They would read something like, "Altitude: From 5000 feet up to and including 17999 feet MSL."

Yes. The TFR over Beale Air Force Base (BAB) is defined as:

From and including 4100 feet MSL up to and including 18000 feet MSL.

Note how this TFR is essentially an extension of the Class C airspace from its charted ceiling up to the beginning of Class A airspace. The requirements to enter the TFR are just: Be on an ATC-assigned discrete code, and maintain two-way comms with ATC.
Note also that this is one of many "temporary" flight restrictions which are in reality quite permanent. It isn't so permanent as, for example, the Disneyland and Disney World "T"FRs, which are so permanent that they're highlighted on the printed VFR sectional. But the Beale "T"FR does get re-issued every six months or so.
This is the exception which proves the rule; I'm not aware of any other TFRs which begin higher than the surface.

Another current example is https://tfr.faa.gov/save_pages/detail_4_4753.html: it has a small surface area and a larger area that starts at 2400 MSL. Kind of like a typical class C airspace shape but less circular.

Another example with no surface area is https://tfr.faa.gov/save_pages/detail_4_4792.html. Seems they're not especially rare!


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Dimension spar webs and spar caps
Hello aviation community!
I would like to ask how one proceeds with dimensioning the spar caps and spar webs of a wing? As in the process of doing so.
This is just based on some experimental calculation for a small UAV aircraft I am doing as a project. All we know is that we are using a an airfoil of NACA 4412 type. And it would be made of a CFRP material. And also that we would only have one spar, most likely in I-beam form going throught the wing.
So what would your process be or what would you recommend me to do?

Small UAV sized aircraft benefit from squared-cubed scaling laws in a way that the size of the structure is seldom determined by traditional calculations based on flight loads.  Instead, they are typically sized by minimum gague (the smallest amount of material you are willing to use given your processes) and/or handling loads -- the loads exerted on the aircraft by handling -- picked up, put down, thrown in the back of a car, assembled, disassembled, dropped, etc.


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Torsional Moment using Pitching Moment Distribution
Hello aviation community!
I have a question regarding my calculation steps for determining the torsional moment and torsional angle deformation.
So the main goal is to find the torsion deformation distribution along the wing span using this formula:
$$\frac{d\phi}{dx} = \frac{M_T}{G \cdot I_T}$$
X is along wingspan direction. But in order for me to integrate this, I first need the torsion moment $M_T$. I therefore need its distribution along the wing, and is therefore again a function of x. This is the formula we have used:
$$M_T = \frac{1}{2}\cdot \rho \cdot u^2 \cdot C_m \cdot S \cdot l$$
From my understanding of this formula, the only thing that changes spanwise is the lever arm at between the lift and the aerodynamic center along the wing's cross-sectional area's plane $l$. Therefore, the torsion moment function becomes:
$$ M_T(x) = \frac{1}{2}\cdot \rho \cdot u^2 \cdot C_m \cdot S \cdot l(x)$$
This is where I believe my thinking process became wrong: I assumed that $l(x)$ is just the chord distribution along the wing span (we have an elliptical wing btw, so we're using this formula we found in one of Raymer's book):
$$l(x) = C(x) = \frac{4 \cdot S}{\pi \cdot b} \sqrt{1 - (\frac{2x}{b})^2}$$
I then plugged it into the $M_T(X)$ equation, which I then plugged back into Bredt's formula and get this:
$$\frac{d\phi}{dx} = \frac{\frac{1}{2}\cdot \rho \cdot u^2 \cdot C_m \cdot S \cdot \frac{4 \cdot S}{\pi \cdot b} \sqrt{1 - (\frac{2x}{b})^2}}{G \cdot I_T}$$
And so I tried to integrate this and you'd get this:
$$\frac{2C_{m} S^{2} u^{2} {\rho} \left(\frac{b \arcsin\left(\frac{2x}{b}\right)}{4} + \frac{x \sqrt{1 - \frac{4x^{2}}{b^{2}}}}{2}\right)}{\pi \cdot GI_{T} b} + C$$
But at this point, I do not know what C should be, and I also do not know if I am even doing this correctly. How do I find the torsion moment distribution $M_T(x)$ and the torsional deformation deformation $\phi(x)$?
It would be great to get some help on this.

"From my understanding of this formula, the only thing that changes spanwise is the lever arm at between the lift and the aerodynamic center along the wing's cross-sectional area". I think you wanted to say "the lever arm between the lift and the torsional center". Plus, you are speaking about lift but your equation is about aerodynamic moment

@sophit, Yes, you are correct that I meant to say the lever arm between the lift and the torsional center, but this changes along the wing span of an elliptical form, right? If so, I am not sure how to approach this...

Why should it change? Lift acts more or less at the quarter chord point and a wing is normally built so that its torsional center is at the same location so that the lever arm is basically zero. If the airfoil is symmetrical then also its pitching moment is zero.


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Is the fuselage of the CEA 311 Anequim configured as elliptical?
I am currently studying the effects of reduced drag induced by laminar flow on the subsonic aircraft. In order to complete that, I have believed I found the optimal fuselage which has the best favorable pressure gradient. This fuselage is the NACA 66, which looks like an elliptical format.
Now I am here to ask you guys,

Is this CAE 311 fuselage elliptical?
Thanks for the answer!

If you want laminar flow over the forward fuselage, remove the propeller.
The wake of the propeller will trip flow immediately. Laminarisation is the reason for the fixed front part of the canopy on some gliders: Along the gap between the moveable canopy and the fuselage a wedge of turbulent flow develops which can only be avoided by a very smooth and gapless surface.

DG-100 forward fuselage (picture source). The two-part canopy was inspired by the hope of keeping flow laminar. Later versions changed to a single-piece canopy.
To answer your question: In my understanding the "elliptical" in elliptical fuselage refers to its cross section, not the profile in side view. Except for the two side bubbles of the canopy, your design has indeed an elliptical fuselage.


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How to calculate lift coefficient using pressure distribution?

Above is the image of the question I want to ask. Please clarify on how the pressure coefficients of the upper and lower surfaces of an airfoil can be used, also if there is a set equation to calculate this lift coefficient.

The exact way to calculate was not provided. Just wanted to know how it would be calculated. @Bianfable

Maybe the discussion in this Q&A helps: How are Cd and Cl calculated from Cp data?

I have looked through that discussion, but I can't seem to use the Xfoil software @Bianfable

Pressure is defined as the force applied perpendicular to a surface divided by the surface's area.
In order to go from the pressure coefficient to the (aerodynamic) force coefficient, one simply have to multiply the former by the surface.
In this particular case this can even be done manually, taking into account that:

an airfoil is considered in the text; that means that we are dealing with a pure 2D body and therefore a wing area cannot be really defined; instead, we consider as our area only the length along the chord (i.e. we suppose that the wing possesses a unitary span);
the shape of the airfoil is not know; that means that also the direction perpendicular to it is not know; anyway as a first approximation we can consider that the surface of an generic airfoil is practically horizontal everywhere except close to the leading edge; therefore the relevant aerodynamic force is basically vertical everywhere and then it goes in the development of lift (except close to the leading edge, where it mostly goes in the development of drag; anyway we focus here only on lift).

With those two points in minds, the value of the lift coefficient becomes:
$C_l=\text{ sum of }(C^i_{p,low}-C^i_{p,upp})c^i$
where "$^i$" means the local i-th station along the chord, from 0 to 14 as given in the text. $c^i$ is the local "surface" (piece of chord) and can be approximated with the distance between two stations, that is 0.02 for the firsts 6 stations and 0.1 afterwards. As said, the value at chord=0 is not considered in the calculation of the lift since it contributes almost exclusively to the drag and therefore we start from 1:
$C_l=(0.54--1.35)\cdot0.02+(0.54--1.512)\cdot0.02+ ... +(0.1404--0.27)\cdot0.1=1.3$
For a standard NACA 2412 this corresponds to an $\alpha$ of some 10°.


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Air Pollution and High Pass engines
If Air is use. “High Bypass Turbines”.  Where does air pollution come in that is mentioned frequently by Politicians and media
I’m a total layman at this

Fuel is used to turn the fan which pushes air. What don't you understand?

Welcome to Aviation.SE! Can you phrase your question in complete sentences? It's hard to understand what you want to know like this. Please have a look at the answers to What is the difference between turbojet and turbofan engines? and then edit your question to include what's still unclear to you.

All turbine engines regardless of specific type burn hydrocarbon-based fuel (kerosene, basically) in order to generate propulsion. The burning of these fuels creates carbon dioxide as a byproduct, which is a pollutant.


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How much energy per second would a nuclear reactor need to power a fighter jet?
Fighter jets typically require high amounts of thrust compared to other aircraft. Lets take the F-22 for example, and lets assume the F-22 powered by a nuclear reactor and the F-22 powered by a traditional engine both weigh the same. How much capacity would a nuclear reactor (fusion or fission) need to produce the same amount of thrust as an F-22 engine by heating up the air coming through the intakes?

One way to approach this is to estimate a maximum total fuel flow rate (e.g., lbm/sec) and multiply that by the specific energy of the fuel (e.g., J/lbm). Wikipedia says the Raptor uses JP-8.

Only if you use the nuclear reactor to refine JP-8....

energy per second is power

Turbofans are built to mainly deliver thrust not power so that it's a bit difficult to convert their thrust in equivalent power.
But as a workaround we can consider a turbofan which is both used to deliver thrust on an airplane and power on a power plant: the GE CF6 is a good example.
Used as jetliner engine, it can deliver 230 to 275 kN thrust; used as power generator, it can deliver 40 to 56 MW.
The two Pratt & Whitney F119-PW-100 powering the F-22 deliver a total of 230 kN thrust dry and 310 kN with afterburner. Being in the same range as the CF6 we can assume that you need a nuclear reactor generating a peak power of some 60 MW.
Something like this should "fit" the bill...

This doesn't directly answer your question of "How much energy..", but this was thought of, tried, and discarded in the 40's and 50's.

One inadequately solved design problem was the need for heavy shielding to protect the crew and those on the ground from radiation; other potential problems included dealing with crashes.

Your assumption of "both weigh the same" can't happen, if you wish the aircrew to live.

Thanks for the reply. Yeah, i know the weight would most likely not be the same, I was mostly just brainstorming a reality in which it was. Damn you physics!

The crew doesn't have to live in the same state, however.


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When was the pitot-based ASI first used on aircraft?
The pitot was first invented well before aircraft, yet early aircraft lacked an airspeed indicator (ASI). What aircraft first had a pitot-based ASI, and when?

The earliest actual use in aircraft that I can find are in August 1912:
https://www.flightglobal.com/pdfarchive/view/1912/1912%20-%200746.html
https://www.flightglobal.com/pdfarchive/view/1912/1912%20-%200840.html

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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What is the origin of the practice of numbering runways by magnetic heading?
Today, runways are always named according to the magnetic heading. How did this practice start? When and where was the practice invented? Whose idea was it, and how did it catch on?

Related: First Paved Airport: Ford's Airport:
and more reading.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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How does the velocity of a turboprop engine relative to the airplane change when a plane is banking?
I saw this YouTube video recently:

And in it, a turboprop engine propeller and gearbox comes out and slashes across the underbelly of the plane, crippling the aircraft. My question is, what aerodynamic force is involved with the turboprop + gearbox being able to fall out specifically during the turn? I can imagine that for whatever reason, when the pilot decided to quickly turn around and head back, that the outermost turboprop must have been moving slower than the plane, and that those forces caused by the turn ultimately tugged the propeller out, and that the turning of the plane brought the propeller under the plane causing the massive damage.

Why not ask instead, "What is the formula for the difference in airspeed between the inboard and outboard wingtips, as a function of airspeed (as measured at the fuselage) and bank angle?"  You'll find the answer is rather small value during high-speed flight.

Well I don't really know much about how airplanes work and I just wasn't sure of how a propeller can lift out of a turboprop so I thought I'd ask here alongside my best assumption as to what was going on. So I'm assuming then that the turboprop didn't lift out because of the turn.

This question is "low hanging fruit" ripe for someone to pick-- but everyone seems to be sleeping-- but the very brief answer (I would post it as such if the question weren't so full of misconceptions) is a) there's no hint in the video that any pilot action caused the problem, and b) you can be sure that no roll rate (rate of change in bank angle), and no bank angle (steepness of "tilt") that this aircraft was capable of in normal non-violent-nausea-inducing operations ,could have remotely possibly have been the cause of this structural failure, absent some pre-existing flaw or failure.

Note:  The video is not available in all locations worldwide.

In a coordinated turn, this is purely a geometry question. Let's call the distance from centerline to engine $d$. The plane must bank to allow for centripetal acceleration $a=v^2/r$ with $v$ true airspeed and $r$ turn radius. This places the engines at a lateral distance of  $$d^*=\frac{d}{\sqrt{1+\frac{a^2}{g^2}}}$$
from the centerline with $g$ acceleration due to gravity. Finally, the speed of the inner engine is $v_1=v(1-d^*/r)$ and the outer engine $v_2=v(1+d^*/r)$. The speed difference is thus $$\delta=\frac{2vd^*}{r}.$$ If you want you can simplify this to $\delta=\frac{2gvd}{\sqrt{g^2r^2+v^4}}$
You may play around with some real world values, but it's safe to say that no turn will rip off a turboprop engine just from the speed difference - these things are designed to apply many kilonewtons of thrust, also in reverse.

Or course we could also consider the (vertical) velocity component imposed by rolling (changing bank angle) -- but we all know this is all a moot point in relation to this particular in-flight incident--

If the turn forces did not dislodge the prop, what did?
After that great crew brought their plane to a stop, the maintenance records for #4 engine may have been first on their minds, after safely deplaning the passengers.
When one considers the props pull the plane along, then what ever bearing that holds that (turbo) prop to its gear case comes into focus.  If that bearing fails, the prop will literally pull itself ahead and out of the nacelle.
The rest is seen in the video.  Normal turning forces, with passengers comfort in mind, cannot be expected to cause that type of failure.
With the huge propellers that drove that plane, any imbalance in the prop assembly could cause them to "wobble", weakening surrounding structures to the point of failure. This type of accident was all too common in the early age of passenger travel. In the video, one can see an unusual shudder in the co-pilot's control column and the captain making a decision to abort the flight, turn around, and get the plane back on the ground (before all hell literally broke loose).
Stringent quality control and maintenance procedures, along with proper design, are key factors in prevention of this type of accident.


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Are Airbus A320 Cabin Door Exterior & Interior Levers Linked?
Was looking at this video on Airbus A320 Cabin door procedures and was wondering if the exterior door lever is mechanically linked to the interior lever? It seems as if the exterior lever will open the interior lever but I am unclear on if they are 1:1 linked and always opening/closing one will open/close the other.
Video:

Interesting question! Welcome to Av.SE.

Operating interior lever will not open exterior lever. No source besides experience, though.


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Is there much point to getting a sport pilot license if you don't intend to buy a Light Sport Aircraft?
It seems difficult, if not impossible to rent a Light Sport Aircraft, hence my question.  Unless you had a friend with an LSA it wouldn't be much use to hold that license, would it?

Its not impossible to rent an LSA.

Where are you trying to rent an LSA?

This is in the north Houston area.

You can find light sport airplanes for rent. They may not be at every flight school or FBO, but they are out there and they are available.
I find both the sport pilot and recreational pilot certificates to be a bit useless, the latter is definitely such because there are only about 600 license recreational pilots in the United States at this time. Originally, the sport pilot certificate was created as an economical entry into general aviation, aircraft ownership and future ratings.  Sadly, this proved to be a great disappointment caused by a myopic study of the general aviation market. Most LSAs purchased today are done so buy commercial or airline transport rated pilots as a light airplane to fly around locally on the weekends and come fully equipped IFR-capable glass cockpits, digital autopilots, BRS parachutes - the works. Prices now range from 170,000 to a whopping 380,000 in the case of an Icon A5 - a far cry from the simple day VFR inception of the LSA with minimal avionics.
As for the usefulness to a light supports pilot certificate, they can be used, but require additional training and logbook endorsements in order to fly cross country or at night, etc.  personally if you really want to use a pilots license to travel around the country or to different destinations, you will want to obtain a private pilot certificate. It offers the least restrictions short of commercial flight operations.

The training requirements and checkride are nearly the same for Sport and Private, and getting a Sport license first doesn’t help at all if you later upgrade to Private. The only difference is the latter requires you pass at least one class 3 Medical exam, and the former only requires you to have a current DL.
If you worry that you can’t pass that one medical exam but haven’t yet been denied, then yes, there’s a point to getting a Sport license: it’s your only option if you want to be a pilot.
LSA rental options are indeed currently fairly limited, but that will presumably change over time—especially if the proposed weight limit increase ever gets adopted—and your license is good for life.
Also, you can look into creating a club or partnership with other Sport pilots in your area to buy an LSA.  Any school that does Sport training should be able to help get their graduates connected for such a purpose.